Description: The long-term objective of this research project is to develop a detailed atomic-resolution structural and functional understanding of protein aggregation and fibrillation relevant to human disease, principally with studies of alpha-synuclein. Wild type alpha-synuclein and its mutants (A30P, E46K and A53T) associated with early-onset Parkinson's disease (PD) will be examined in several structural states, including protofibrils, fibrils and membrane-associatedcomplexes. We propose that the chemical details of these structures determine the natural physiological function of alpha-synuclein and, in the mutants or under environmental stress, contribute to PD pathology. Moreover, we propose that conversion among several structural states is an essential feature of synucleins; this structural plasticity is likely to be required for neuronal development and maintenance. To examine these structures, magic-angle spinning (MAS) solid- state NMR (SSNMR) experiments will be employed, elucidating details of covalent chemistry, conformation and dynamics that are inaccessible to other experimental techniques. Complementary analysis and characterization techniques will include kinetic measurements (by thioflavin T fluorescence, light scattering and sedimentation analysis), high-resolution mass spectrometry, atomic force and electron microscopy, solution NMR and phage display. We will leverage these technologies along with sample preparation and isotopic labeling strategies to improve our understanding of protein aggregation relevant to disease in the specific case of alpha-synuclein, including: (1) the fundamental biophysical principles of alpha-synuclein aggregation and membrane association, (2) specific structural information that will enable rational design strategies for small molecules that modulate alpha-synuclein function and/or serve as diagnostic tools for PD, and (3) elucidation of specific structural interactions between alpha-synuclein and other brain proteins. Relevance to public health: Alpha-synuclein is a central player in Parkinson's disease. The precise relationships between alpha-synuclein structure and this disease are not yet well understood. Our proposed studies aim to advance this fundamental knowledge, which will assist the broader research community in developing improved diagnostic tools and therapies for Parkinson's disease.